The unfolding revolution wrought by unmanned aerial vehicles has freed a number of military missions from the tyranny of human endurance. Plinking terrorists no longer requires an aircraft with oxygen flowing into the cockpit, parachutes or other gear necessary to ensure a pilot’s survival.

But another limit still exists.

When MQ-1 Predators are armed, they head off into the wild blue yonder with a lone pair of Hellfire missiles under their wings. It’s a double-barreled shotgun you can’t reload.

But folks at General Atomics are getting increasingly excited by the HELLADS — the High-Energy Liquid Laser Defense System. It is designed to shrink a flying laser into a package small enough to cram into an aircraft.

“It would give us an unlimited magazine,” says one person close to the program. There’s talk that it could be fielded within five years.

In other words, an unmanned aircraft could not only give U.S. forces a so-called “persistent presence” overhead, it wouldn’t have to return to base after firing its pair of missiles for lack of additional firepower.

According to this General Atomics video, putting the laser on the company’s Predator C Avenger is a match made in heaven. The jet-powered Avenger is bigger and faster than either the company’s Predator or Reaper drones. It boasts of the “attrition tolerance” of unmanned aircraft, which is one way to put it. (These weaporn videos are becoming ever more Hollywoodesque, down to stirring music, rapid-fire editing and apparently a corps of actors ready to spout lines like: “Target destroyed.”)

Last year, General Atomics landed a $40 million contract from the Defense Advanced Research Projects Agency to continue to refine, shrink and power up HELLADS. Its 150-kW solid-state power would supposedly be capable of downing aircraft.

But lasers — even tiny ones — have bad as well as good points. Downside: they’re line-of-sight weapons, so they’re not like fire-and-forget missiles that home in on the heat or radar return generated by a target. And they don’t work so well through haze, dust or the fog of war. Upside: they travel at the speed of light, so jinking to avoid being hit (assuming the target is an aircraft) really isn’t an option.

There’s another challenge as well: laser weapons — death rays, if you prefer — have always been just out of reach. The joke is that they’re only five years into the future — and always will be. Whether or not this latest version turns out any different remains an open question.

There are also bigger issues associated with such weaponry. Some legal scholars, and military officers, assert that drone killings are too easy to order, are illegal, shouldn’t be conducted in secret by the CIA and, at the end of the day, generate a dozen terrorists for every one that’s killed.

All that may be true, but it also misses a key element of having drones orbit silently overhead, able to blast the enemy repeatedly with their laser weapons. The real problem, of course, isn’t a lack of Hellfire missiles. The challenge is knowing where to aim them. Swapping Hellfires for lasers won’t change that.